In networks using wireless technology, a configuration method is widely known in which each terminal performs information transfer by a subordinate of a control station called an “access point” or the like. Each terminal station performs wireless communication, while synchronizing via the access point. For example, a terminal station reserves a necessary band for information transfer, and uses a channel so that a collision with information transfer of other terminal stations is not produced. However, in such a configuration method of a network, it may be necessary to perform wireless communication via the access point, even at the time when performing asynchronous communication among terminals, and there will be the problem of the utilization efficiency of the channel being reduced by half.
In contrast to this, “Ad-hoc communication”, in which terminal stations perform direct and asynchronous wireless communication not via an access point, has been devised as another configuration method of a wireless network. For example, in an IEEE802.11 type wireless Local Area Network (LAN) system, in addition to an infrastructure mode in which an access point intervenes, an Ad-hoc mode is prepared in which each terminal station is operated by Peer-to-Peer with autonomous distribution, without distributing an access point.
In an Ad-hoc network, there is no means for synchronizing between terminal stations, such as an access point. Accordingly, it may be necessary to avoid competition, at the time where a plurality of terminal stations use a same channel Carrier Sense Multiple Access (CSMA) is known as a representative access system which avoids competition. In CSMA, a terminal station with transmission information avoids collisions by a procedure, which confirms an occupancy state of a media before transmission, and starts transmission in the case where the media is clear.
Further, in CSMA, there is the problem of hidden terminals. Here, a hidden terminal is a terminal station in a state where mutual wireless signals do not arrive. Since a carrier of a hidden terminal is not able to be detected, a collision with a hidden terminal is not able to be avoided by only CSMA.
RTS/CTS has been devised as a method which avoids collisions with hidden terminals. A communication station of a transmission source transmits a transmission request packet Request To Send (RTS), and starts data transmission by replying to a confirmation notification packet Clear To Send (CTS) received from a communication station of a data transmission destination. Also, since a hidden terminal can receive at least one of a RTS and a CTS, a collision is avoided, by setting a transmission stop period of the station itself only for the period in which it is assumed that data transfer is performed based on RTS/CTS.
However, in an access system based on CSMA, there will be the problem of a transmittable opportunity being reduced in accordance with the number of terminal stations attempting to perform information transmission on a same channel, even if a collision such as described above can be avoided. In the case where a certain terminal station does not want to perform communication with a terminal station, where a path loss with this terminal present at an extremely adjacent location is remarkably small compared to a path loss with other stations, transmission for collision avoidance will not be permitted, when receiving a signal of another terminal station (for example, refer to Patent Literature 1). That is, when a traffic amount increases on a channel, the interference amount to an adjacent terminal station will increase, and the band used by the adjacent terminal station will be limited.